1. Field of the Invention
The invention relates to a method of manufacturing a light emitting device using a phosphor sheet.
2. Description of the Related Art
A light emitting device is known in which the phosphor sheet obtained by processing a phosphor containing resin into a sheet is disposed on a light emitting surface of a light emitting element such as a light emitting diode (LED) chip is known. In the light emitting device, a color of a light emitted from the light emitting element and transmitted through the phosphor sheet is mixed with a color of a light emitted from the phosphor in the phosphor sheet so as to produce an emission color of the light emitting device.
In the above light emitting device, the phosphor is dispersed in a whole thickness direction of the phosphor sheet. Among lights emitted from the light emitting element and passing through the phosphor sheet, with regard to the amount of phosphor-wavelength converted light, light emitted in a direction inclined from immediately above the light emitting element is higher than light emitted immediately above the light emitting element. This is because the light emitted in the inclined direction has longer distance (i.e., optical path) needed for passing through the phosphor sheet than the light emitted immediately above the light emitting element. Thus, a problem on the dispersion of emission chromaticity may arise due to the difference of emission angle.
To solve the problem, for example, a light emitting device is known which controls the emission chromaticity dispersion caused by the emission angle difference by arranging a phosphor plate which is composed of a base, phosphor and a light scattering material on the light emitting element so as to diffuse the light emitted from the light emitting element by the light scattering material (see e.g. JP-A-2013-153105).
Also, a two layer structure phosphor sheet is known which is composed of a transparent layer and a high concentrate phosphor layer (see e.g. JP-A-2005-24272). According to the phosphor sheet, the phosphor layer is arranged contacting with or coming close to the light emitting surface of the light emitting element. Thereby, the distance of the light emitted from the light emitting element and passing through the phosphor layer can be nearly equalized at any emission angles so as to prevent the emission chromaticity dispersion caused by the emission angle difference.